Normal and dystrophic extraocular muscle will be studied by combined light and electron microscopy. In normal muscle analysis the comparative organization of vertical and horizontal recti would provide information relative to the functional significance of the respective fiber types. The mode of function of these fiber types would also be studied by detailed examination of their innervation in teased preparations with cholinesterase stain. Individual fibers isolated in this manner would in turn be examined by electron microscopy. The above two approaches would then be related to histochemical fiber types, with emphasis on information available from ATPase stains. Mouse strains inbred for Duchenne and myotonic dystrophy will be studied as models of oculomotor disorders of these two varieties. The etiology and progress of these disease processes will be followed over time, with skeletal muscle used as controls. Emphasis will be placed on questions of neuropathic vs. myopathic primacy, as well as on involvement of the vascular system. Fibers will be followed to ascertain the relative involvement of internal cell morphology as opposed to disruption of the neuromuscular junctions. Patterning of different kinds of morphological changes along the fibers length will be related to fiber types and disease entities.